World Trade Center spire

Two people look out at One World Trade Center in New York as seen across the Hudson River in Jersey City, New Jersey, May 10, 2013. The final piece of the building's spire will be attached later this morning. (REUTERS/Gary Hershorn)

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The final piece of the One World Trade Center spire is attached to the building by ironworkers in New York May 10, 2013. (REUTERS/Gary Hershorn)

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The final piece of the One World Trade Center spire is attached to the building by ironworkers in New York May 10, 2013. (REUTERS/Gary Hershorn)

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Two people photograph One World Trade Center in New York as seen across the Hudson River in Jersey City, New Jersey, May 10, 2013. The final piece of the building's spire will be attached later this morning. (REUTERS/Gary Hershorn)

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The final piece of One World Trade Center's spire is seen next to the base of the building before it is lifted to the top in New York, May 2, 2013. Crane operators hoisted the final pieces of the spire on Thursday, helping to fill the void in the New York City skyline that was left by the attacks of Sept. 11, 2001. Ironworkers will finish installing the spire, which weighs about 800 tons (725 metric tons) and is 400 feet (122 meters) tall, at a later date. (REUTERS/Lucas Jackson)

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Ground Zero workers photograph with their phones as the final piece of One World Trade Center's spire is lifted to the top of the building in New York, May 2, 2013. Crane operators hoisted the final pieces of the spire on Thursday, helping to fill the void in the New York City skyline that was left by the attacks of Sept. 11, 2001. Ironworkers will finish installing the spire, which weighs about 800 tons (725 metric tons) and is 400 feet (122 meters) tall, at a later date. (REUTERS/Lucas Jackson)

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A U.S. flag flies in the wind as the final piece of One World Trade Center's spire is lifted to the top of the building in New York, May 2, 2013. Crane operators hoisted the final pieces of the spire on Thursday, helping to fill the void in the New York City skyline that was left by the attacks of Sept. 11, 2001. Ironworkers will finish installing the spire, which weighs about 800 tons (725 metric tons) and is 400 feet (122 meters) tall, at a later date. (REUTERS/Lucas Jackson)

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The steeple of St. Paul's Chapel rises into the sky as the final piece of the building's spire is lifted to the top of One World Trade Center in New York, May 2, 2013. The piece will be attached at a later date. (REUTERS/Lucas Jackson)

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A woman and man (L) embrace as they watch the final piece of One World Trade Center's spire being lifted to the top of the building in New York, May 2, 2013. Crane operators hoisted the final pieces of the spire on Thursday, helping to fill the void in the New York City skyline that was left by the attacks of Sept. 11, 2001. Ironworkers will finish installing the spire, which weighs about 800 tons (725 metric tons) and is 400 feet (122 meters) tall, at a later date. (REUTERS/Lucas Jackson)

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Iron workers wait for the final piece of the One World Trade Center spire to raised into position for attachment to the building, in New York, May 10, 2013. (REUTERS/Gary Hesrhorn)

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Ground Zero workers watch as the final piece of One World Trade Center's spire is lifted to the top of the building in New York, May 2, 2013. Crane operators hoisted the final pieces of the spire on Thursday, helping to fill the void in the New York City skyline that was left by the attacks of Sept. 11, 2001. Ironworkers will finish installing the spire, which weighs about 800 tons (725 metric tons) and is 400 feet (122 meters) tall, at a later date. (REUTERS/Lucas Jackson)

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A U.S. flag flies on a building behind workers from the Ground Zero site as they prepare the final piece of One World Trade Center's spire to be lifted to the top of the building, in New York May 2, 2013. Crane operators hoisted the final pieces of the spire on Thursday, helping to fill the void in the New York City skyline that was left by the attacks of Sept. 11, 2001. Ironworkers will finish installing the spire, which weighs about 800 tons (725 metric tons) and is 400 feet (122 meters) tall, at a later date. (REUTERS/Lucas Jackson)

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A worker from Ground Zero attaches straps to the final piece of One World Trade Center's spire as it is prepared to be lifted to the top of the building in New York, May 2, 2013. Crane operators hoisted the final pieces of the spire on Thursday, helping to fill the void in the New York City skyline that was left by the attacks of Sept. 11, 2001. Ironworkers will finish installing the spire, which weighs about 800 tons (725 metric tons) and is 400 feet (122 meters) tall, at a later date. (REUTERS/Lucas Jackson)

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The final section of the spire that will top off One World Trade Center is raised past iron workers to the top of the building in New York, May 2, 2013. The piece will be attached at a later date. (REUTERS/Gary Hershorn)

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A U.S. flag flutters in the wind as the final piece of One World Trade Center's spire is lifted to the top of the building in New York, May 2, 2013. Crane operators hoisted the final pieces of the spire on Thursday, helping to fill the void in the New York City skyline that was left by the attacks of Sept. 11, 2001. Ironworkers will finish installing the spire, which weighs about 800 tons (725 metric tons) and is 400 feet (122 meters) tall, at a later date. (REUTERS/Lucas Jackson)

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The final section of the spire that will top off One World Trade Center is raised to the top of the building in New York, May 2, 2013. Crane operators hoisted the final pieces of the spire atop One World Trade Center on Thursday, helping to fill the void in the New York City skyline that was left by the attacks of September 11, 2001. (REUTERS/Brendan McDermid)

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A U.S. flag flutters in the wind as the final piece of a spire is lifted to the top of One World Trade Center in New York, May 2, 2013. The piece will be attached at a later date. (REUTERS/Lucas Jackson)

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Iron workers wait for the final piece of the One World Trade Center spire to be placed into position for attachment to the building, in New York, May 10, 2013. (REUTERS/Gary Hershorn)

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A ferry makes its way across the Hudson River as the sun rises between One World Trade Center (C) and the Empire State Building (L) in New York as seen from Jersey City, New Jersey, May 10, 2013. The final piece of the building's spire will be attached later this morning. (REUTERS/Gary Hershorn)

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One World Trade Center in New York is reflected in the Hudson River as seen from Jersey City, New Jersey, May 10, 2013. The final piece of the building's spire will be attached later this morning. (REUTERS/Gary Hershorn)

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Iron workers wait for the final piece of the One World Trade Center spire to be brought to them for attachment to the building, in New York, May 10, 2013. (REUTERS/Gary Hershorn)